Due to the rising costs of fossil fuels, the selection and implementation of an inexpensive and reliable source of energy have been a challenge for many developed countries.
A hybrid geothermal/photovoltaic (GPV) power plant takes advantage of the readily available solar energy prevalent in arid areas such as the Middle East and Africa and of the costs of photovoltaic cells that are continuously being lowered, while exploiting the sustainability of geothermal power during cloudy days or during the nighttime, to provide constant near to maximum power generation without being subject to solar-specific restrictions.
A significant problem related to GPV power plants is in terms of energy storage. Due to the variability of solar energy, the direct current (DC) power produced by one or more photovoltaic (PV) modules may be in excess of what is needed by a utility. The excess generated power at times therefore has to be suppressed since it cannot be economically stored, resulting in a substantial loss of revenue. On the other hand, geothermal energy is also not readily storable due to the substantially constant flow of the geothermal resource.
In one prior art GPV power plant, a geothermal power conversion unit and a PV power conversion unit are connected in parallel to a generator for supplying alternating current (AC) electrical power to the electric grid. That is, the power extracted from the geothermal unit drives a turbine coupled to the generator while the DC electrical power produced by the PV unit is converted into AC power by means of an inverter. An inverter comprises expensive electric and electronic components that are subject to unreliable operation, and requires power factor control to match the phase of the AC power produced by the inverter to the phase present on the electric grid. During periods of surplus PV-derived electrical power, the excess electrical power is stored by an expensive and complex battery storage system, requiring switches to be driven when the voltage at the battery terminals has reached a high voltage or alternatively a low value, and a unit to manage the charge and discharge cycles of the batteries.
It is an object of the present invention to provide a hybrid geothermal/photovoltaic power plant that produces a substantially uniform electrical output.
It is an additional object of the present invention to provide energy storage for generated power in excess of what is needed by a utility, essentially without use of a battery storage system or a separate heat storage medium.
It is an object of the present invention to provide a hybrid geothermal/photovoltaic power plant by which the generated DC power is converted to AC power without use of an inverter.
Other objects and advantages of the invention will become apparent as the description proceeds.